1. Field of the Invention
The present invention relates to an image forming device, and more particularly to an image forming device that includes a pair of guide plates that guide transfer media transported upward from resist rollers to a transfer position between an image support member on which toner images are formed and a transfer member.
2. Background Information
The majority of image forming devices, and in particular color image forming devices such as color copy machines or color printers, are now multi-stage drum type (tandem type) rather than single drum type, and are capable of high speed processing. The image forming units of a tandem type color image forming device are aligned with each other in the direction in which the paper is transported, and are separated by color, e.g., magenta, yellow, cyan, and black. A color toner image is sequentially formed by means of these image forming devices.
Each color image forming unit is arranged opposite an intermediate transfer belt (an image supporting member), and toner images sequentially formed with each color image forming unit will be transferred to the intermediate transfer belt. The intermediate transfer belt endlessly extends around a plurality of rollers. A primary transfer roller, and a secondary roller which forms a transfer position, are arranged on the outside of the intermediate transfer belt. In addition, transfer media will be transported from a media supply unit to the transfer position via a pair of resist rollers. Toner images on the photosensitive drums will be transferred to the transfer media at the transfer position by applying a transfer bias voltage to the secondary transfer roller. Then, in order to accurately transfer the toner images on the surfaces of the photosensitive drums to the transfer medium and obtain a good image, the transfer media transported from the resist rollers must be guided to an appropriate transfer position. Thus, a pair of guide plates are provided on the upstream side in the transfer medium transport direction of the transfer position, and serve to guide the transfer media transported from the pair of resist rollers to the appropriate transfer position.
Recently, there has not only been an increase in the number of copy machines having both copy and print functions, but due to demands for smaller devices and an increase in the speed of image formation, there has also been an increase in devices which have perpendicular transport paths. These types of devices have image forming means, fixing means, and the like that are arranged perpendicular to each other, and transport transfer media upward. With image forming devices having this type of perpendicular transport path, it is often the case that transfer media is not transported in a straight line between the pair of resist rollers and the transfer position. This is done in order to shorten the transport path. In addition, in situations in which the transfer media is resilient and capable of returning to its original shape after being bent, e.g., when the transfer media is thick paper such as cardboard, it will be easy for images formed on transfer media to become blurred due to the fact that the rear portion of each transfer media will spring back to its original shape after it separates from the resist rollers.
A pre-transfer guide device is designed to pivot around the rotation shaft of the secondary transfer roller in order to smoothly pass even resilient transfer media such as cardboard through the transfer position without jamming. In addition, a pre-transfer guide device has been proposed in which a restriction means is provided on the secondary roller side that will restrict the amount of pivot by the pre-transfer guide members.
With the structure disclosed in Japanese Unexamined Patent Application Publication No. H09-240880, resilient transfer media such as cardboard can smoothly pass through the pre-transfer guide device due to the pivoting and retraction of the pre-transfer guide members. When cardboard is to be passed to a transfer location, the secondary transfer roller will be retracted from the photosensitive drum at a distance equal to the thickness of the cardboard. However, when the pre-transfer guide device is designed to pivot around the rotation shaft of the secondary transfer roller, it will often be the case that the pre-transfer guide members will retract from the transfer position at a distance equal to the distance in which the secondary transfer roller is retracted, and thus the transfer media cannot be guided to an appropriate transfer position. In addition, the restriction means that restricts the amount that the pre-transfer guide members can pivot is provided on the secondary transfer roller side. Thus, when transfer media is to be passed through the transfer position, the secondary transfer roller will retract from the photosensitive drum at a distance equal to the thickness of the cardboard, and it will be difficult to restrict the pre-transfer guide members to a predetermined amount of pivot.
Accordingly, an object of the present invention is to provide an image forming device that can control image blurring, image shrinkage, and the like when resilient transfer media such as cardboard is to be transported upward from a pair of resist rollers and guided to a transfer position, and obtain suitable transfer images.
In view of the above, there exists a need for an image forming device which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.